#include <stdio.h>
double average(double a, double b, double c);
int main(int argc, char *argv[])
{
    double x = 5;
    double y = 9;
    double z = 7;
    printf("%.2lf\n", average(x, y, z));
    return 0;
}
double average(double a, double b, double c)
{
    return (a + b + c) / 3;
}
